1. Field of the Invention
The present invention relates generally to optical elements, and more particularly to a non-Lambertian glass diffuser replicated from a master diffuser for use in active lighting applications.
2. Description of the Related Art
Methods for manufacturing and replicating optical components utilizing a master and one or more submasters to achieve a final diffuser product having desired light diffusing characteristics are well known. In many of these methods, the creation of the first generation submaster from the master destroys the master rendering it unavailable for later use. There are also other methods of making a replica of a master which contains optical features identical to that of the master without destroying the master. These other methods are described in one or more pending U.S. applications, referenced below, which are assigned to the assignee of the present invention. However, with each of these methods, the submasters are each made from materials which are not significantly durable or suitable for use under high temperature conditions.
The specific embodiments described below regarding the rubber submaster and the silver and nickel submaster are disclosed in co-pending U.S. application Ser. No. 09/052,586 now U.S. Pat. No. 6,159,398 entitled xe2x80x9cMethod of Making Replicas While Preserving Master,xe2x80x9d commonly assigned to the assignee of the present invention.
One such method involves recording optical features on a photosensitive medium using coherent or incoherent light. The photosensitive medium is then further processed to create a master optical product. A layer of two part silicone epoxy is poured over the master to replicate the optical surface features of the master photosensitive medium in the silicone material. The silicone epoxy layer gets cured at room temperature and becomes rubber. The silicone material is then cured further and separated from the master to obtain a silicone submaster. The soft silicone submaster is then used to make successive generations of submasters or final optical products by covering the soft submaster with a layer of epoxy, covering the layer of epoxy with a plastic substrate, curing the epoxy and separating the epoxy and plastic substrate from the submaster.
Another method of creating a submaster for an optical product involves coating the recorded and developed photosensitive medium master discussed above with a layer of silver instead of silicone. A layer of nickel is electroplated onto the silver layer and then the silver layer and layer of nickel are removed from the photosensitive material or medium to form the submaster. The combined silver and nickel backing form a metal shim submaster which is then used to create final optical products by embossing the surface features of the submaster into epoxies, plastics or polycarbonate materials, or by injection molding such materials into a mold carrying the submaster.
One significant shortcoming with each of these methods is that the final optical products created from the submasters are made from relatively non-durable materials such as plastics, epoxies, or polycarbonate composites. These materials are not suited for use near extremely high temperature light sources and are also not well suited for use outdoors under exposure to cyclical or extreme environmental conditions.
Other commonly assigned U.S. patents and pending applications disclose somewhat related methods for making and recording optical products and replicating those products so that they may be mass produced. For example, U.S. Pat. No. 5,365,354 entitled xe2x80x9cGrin Type Diffuser Based on Volume Holographic Materialxe2x80x9d, U.S. Pat. No. 5,534,386 entitled xe2x80x9cHomogenizer Formed Using Coherent Light and a Holographic Diffuserxe2x80x9d, and U.S. Pat. No. 5,609,939 entitled xe2x80x9cViewing Screen Formed Using Coherent Lightxe2x80x9d, all owned by the present assignee relate to methods for recording and replicating optical products. Each of these U.S. patents is incorporated herein by reference for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art.
Related U.S. patent applications include Ser. No. 08/595,307 entitled xe2x80x9cLCD With Light Source Destructuring and Shaping Devicexe2x80x9d now U.S. Pat. No. 5,956,106, U.S. Ser. No. 08/601,133 entitled xe2x80x9cLiquid Crystal Display System with Collimated Backlighting and Non-Lambertian Diffusingxe2x80x9d now U.S. Pat. No. 5,838,403, U.S. Ser. No. 08/618,539 entitled xe2x80x9cMethod of Making Liquid Crystal Display Systemxe2x80x9d now U.S. Pat. No. 5,735,988, U.S. Ser. No. 08/800,872 entitled xe2x80x9cMethod of Making Replicas and Compositions for Use Therewithxe2x80x9dnow U.S. Pat. No. 5,922,238, and U.S. Ser. No. 09/075,023 entitled xe2x80x9cMethod and Apparatus for Making Optical Masters Using Incoherent Light now abandoned.xe2x80x9d All the above applications are owned by the present assignee and are hereby incorporated by reference for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art.
A primary object of the present invention is to provide a method for making a replica of a master diffuser containing optical features of the diffuser in an extremely durable material such as glass. It is another object of the invention to provide a diffuser made from a material such as glass which is highly durable and suitable for use under extreme conditions such as adjacent a high temperature active light source such as for liquid crystal displays and the like.
In accordance with the present invention, these objects are achieved by a glass optical element having a unitary body structure made from a glass material and at least one optical surface. A surface relief structure is replicated onto the at least one optical surface from a metal submaster optical element. The glass material is first heated to a suitable temperature in order that the glass be softened to a predetermined level of softness. The softened glass is supported on a sturdy support such as a flat metal surface with at least one surface of the glass substrate exposed. The exposed surface is contacted with the surface relief structure of the metal shim submaster optical element for a length of time while pressure is applied to force the metal submaster optical element and softened glass substrate material against one another during at least a portion of the length of time of contact. By the combination of the softness of the glass, the pressure applied between the master optical element, the glass substrate and the sturdy support surface, and the duration of time of such contact and applied pressure, the surface relief structure is replicated in the glass material. The pressure is then released and the master optical element or metal shim and glass material are separated from one another. The glass is then cooled to produce the glass diffuser according to the invention.
The master optical element may in one embodiment be a metal shim having a silver layer backed by a chromium or nickel layer. The silver layer includes a surface relief structure recorded from a photoresist medium by any one of many conventional means. Other master optical elements may be utilized depending upon the particular glass and process characteristics necessary for production of a desired glass diffuser.
The glass substrate material may also be heated utilizing a number of means. For example, the glass substrate material may be placed within a furnace to elevate the temperature of the glass prior to the application of pressure between the glass material and the master optical element. Alternatively, the glass substrate material may be exposed to a direct heat source such as an oxyacetylene flame in order to sufficiently soften an exposed surface of the glass material. In another alternative, a molten glass material may be slightly cooled to a softened state and then contacted with the master optical element during initial manufacture of a glass substrate thereby replicating the surface relief structure directly into the original glass object.
Using this methodology, the assignee has demonstrated the fabrication of glass diffusers in the laboratory. Different types of metals can be used in place of silver, and or nickel-chromium. One alternative choice of such a metal is steel having a higher percentage of carbon. One can also effectively replicate the glass diffuser using a graphite based diffuser master. For example, a diffuser master structure can be ion milled onto the steel metal and/or graphite materials which have thermal expansion coefficients closer to the glass. The use of graphite is critical when a more softened or liquified glass is used.
These and other aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof and the invention includes all such modifications.